The present invention relates generally to magnetic disk drives, and more particularly to a magnetic disk drive having a mechanism for loading and holding a disk inserted with a correct orientation at a predetermined position, and for preventing a disk inserted with a wrong orientation from being loaded into the predetermined position. The term "a correct orientation", as used herein, means the sole orientation in which the disk can be driven at the predetermined position. And the term "a wrong orientation", as used herein, means any one orientation except the correct orientation.
Among magnetic disk drives, hard disk drives have been used as memory means for computers. Hard disks have been more improved than so-called floppy disks in TPI (track per inch) and BPI (bit per inch) so that the hard disks can be recorded with high density. The hard disk is fixed in a sealed-up housing to prevent dust from the outside attaching itself thereto so that it can be recorded with high density.
Consequently, information recorded on the hard disk cannot be used generally except in a computer which includes the hard disk drive. And when the hard disk is overflown, as the disk cannot be easily exchanged, it is troublesome to exchange the hard disk drive itself.
Accordingly, this applicant has developed a disk drive comprising a disk cartridge and a driving device. The term "a disk cartridge", as used herein, means an apparatus which comprises at least a disk and a head in a sealed case, but has no current supply source to drive them and has no controller to control them. The term "a driving device", as used herein, means an apparatus that has the current supply source and/or the controller. The disk cartridge can be easily connected and disconnected from the driving device. The driving device may be connected to an external computer, such as a host computer, and the disk cartridge can be driven and controlled by the driving device and/or the external computer. Therefore the disk cartridge may be considered as being an easily exchangable hard disk.
A conventional magnetic disk drive having a holder in which a floppy disk is inserted is usually equipped with a mis-insert preventing mechanism, as shown in Japanese Laid-Open Patent Application No. 64-30068. The disclosed mis-insert preventing mechanism comprises a floppy disk having a first corner chamferred with a different angle from other chamferred corners and a stopper located in the holder having an inclined plane engagable only with the first corner. The floppy disk can be loaded into a predetermined position only when the first corner is engaged with the stopper. Therefore, when the floppy disk is to be inserted with the wrong orientation, it is blocked from being inserted any more because the inclined plane is not engaged with one of the other corners. On the other hand, in the conventional magnetic disk drive the holder usually decends with the floppy disk so as to be held by a holding mechanism which is provided in addition to the mis-insert prevent mechanism.
Therefore, it is difficult to miniaturize the conventional magnetic disk drive including two individual mechanisms, the mis-insert preventing mechanism and the holding mechanism and a holder movable upward and downward. In addition, the disk cartridge developed by the applicant must be miniaturized and thin. However an effective mis-insert preventing mechanism and holding mechanism have not been suggested in a magnetic disk drive in which a holder is fixed.